1. Field of the Invention
The present invention generally relates to eye tracking systems and, more particularly, to an improved pupil detection system which enhances the operation and reliability of the eye tracking system.
2. Background Description
In any eye tracking system such as the Fitness Impairment Tester disclosed in U.S. Pat. No. 5,422,690 to Tom Cornsweet, a critical capability is to determine if the signal at the detector is that of a pupil. Images other than a pupil occur prior to the start of tracking, in the event that tracking is lost or as a result of a blink. The actions taken in each of these cases is different.
In the tracking system described in U.S. Pat. No. 5,422,690, pupil recognition and blink detection are separated. Pupil recognition is based on image focus and pupil size (based on camera data) and brightness data from a quad detector. Since the focus and pupil size data were derived from a camera, a pupil detection could only be updated at the camera frame rate of 60 Hz. This low update rate limited the ability to actively search for the pupil at the beginning of a test. In addition, dependence on good focus placed significant constraints on the optics path.
While this arrangement could, in principal, detect blinks, it was not fast enough to be used to disable tracking (which operates at &gt;600 Hz) during a blink. As a result, a blink detection scheme based solely on quad detector data was used. That scheme used the fact that the light level at the quad detector usually changed significantly during a blink. Although effective to detect most blinks, this method often detected phantom blinks. These phantom blinks occurred when, as the eye moved, the amount of light reflected by the retina changed as different retinal areas were illuminated by the incident infrared (IR) light. In these cases, tracking would often be lost since tracking was disable during these periods.